Navigation track correction

1. A method comprising: receiving signals, in a receiver from a transmitter, along a traveled path, wherein the traveled path is a path actually traveled by the receiver; storing, in a memory, a first estimated track, wherein the first estimated track includes an estimate of the traveled path of the receiver, recording, in a memory, signal power levels of the received signals, wherein the signal power levels include a first measured signal power level measured at a first time and a second measured signal power level measured at a second time, wherein the first time is before the second time; associating, in the memory, the first measured signal level power with the first time and associating the second measured signal power level with the second time; identifying, by a processor, an extracted change between the first measured signal power level associated with the first time and the second measured signal power level associated with the second time, wherein the extracted change is caused by a propagation path between the transmitter and the receiver transitioning from an unobstructed propagation path at the first time to an obstructed propagation path at the second time as the receiver moves along the traveled path from the first time to the second time, associating, in the memory, a first location on the first estimated track with the extracted change; storing, in the memory, a model including a model of an obstruction and a model of the transmitter; simulating, by the processor and based on the model, modeled signals from the model of the transmitter to points along the first estimated track to generate expected signal power levels of the modeled signals; identifying, by the processor, an expected change of the expected signal power levels, wherein the expected change is caused by a modeled propagation path transitioning from a modeled obstructed propagation path to a modeled unobstructed propagation path, storing, in the memory, an association between a second location on the first estimated track with the expected change; identifying, by the processor, the expected change as corresponding to the extracted change; generating a second estimated track, wherein the second estimated track is an estimate of the traveled path, based on the first location on the first estimated track associated with the extracted change and the second location of the first estimated track associated with the expected change; and storing the second estimated track in the memory, wherein the second estimated track includes smaller positional errors than the first estimated track relative to the traveled path.

2. The method of claim 1 , wherein the model of the obstruction includes a two-dimensional model of the obstruction.

3. A method comprising: receiving signals in a receiver from a transmitter, along a traveled path, wherein the traveled path is a path actually traveled by the receiver; storing, in a memory, a first estimated track, wherein the first estimated track includes an estimate of the traveled path; recording, in the memory, signal power levels of the received signals; identifying, by a processor, an extracted feature of the signal power levels, wherein the extracted feature is caused by a propagation path between the transmitter and the receiver transitioning from a first propagation path to a second propagation path as a result of the receiver having traveled from a first point on the traveled path to a second point on the traveled path, wherein the first point is different than the second point; generating, by the processor, expected signal power levels of the received signals based on the first estimated track of the traveled path; generating, by the processor, a second estimated track based on the recorded signal power levels, the expected signal power levels, and the extracted feature; and storing, in the memory, the second estimated track, wherein the second estimated track is more accurate than the first estimated track relative to the traveled path.

4. The method of claim 3 , wherein receiving the signals along the traveled path includes receiving the signals over a period of time, wherein recording signal power levels of the received signals includes recording the signal power levels of the received signals over the period of time, and wherein the extracted feature is caused by the signals having traveled different propagation paths to two different points on the traveled path at two different times.

5. The method of claim 4 , further comprising: identifying an expected feature based on the expected signal power levels; determining a track bias based the extracted feature and the expected feature; and generating the second estimated track based on the track bias.

6. The method of claim 5 , further comprising identifying extracted features of the signal power levels, wherein the extracted features are caused by the signals having traveled different propagation paths to the traveled path; identifying expected features based on the expected signal power levels, wherein determining the track bias includes determining the track bias based the extracted features and the expected features; and generating the second estimated track based on the track bias.

7. The method of claim 6 , wherein each of the extracted features is caused by the signals having traveled different propagation paths from a same transmitter to the traveled path; and wherein determining the track bias comprises determining the expected features that correspond to the extracted features.

8. The method of claim 7 , further comprising: determining lines of position (LOPs) based on the expected features or based on the extracted features; advancing one or more of the LOPs based on locations associated with each of the extracted features; and determining the track bias based on the LOPs.

9. The method of claim 8 , further comprising: determining the track bias based on an intersection of two of the LOPs, or, determining the track bias based on an intersection of three or more of the LOPs and determining a confidence level of the track bias based on a distance between intersections of different pairs of the three or more of the LOPs.

10. The method of claim 6 , wherein identifying an extracted feature of the signal power levels further comprises: detecting an increase in the signal power levels indicating shifts in the propagation paths of the signals, wherein the increase in the signal power levels is indicative of an obstruction of one of the propagation paths relative to another one of the propagation paths, or detecting a decrease in the signal power levels indicating shifts in the propagation paths of the signals, wherein the decrease in the signal power levels is indicative of an obstruction of one of the propagation paths relative to another one of the propagation paths.

11. The method of claim 10 , wherein further comprising: recording polarity of the received signals; and identifying an extracted feature of the polarity of the received signals, wherein the extracted feature of the polarity of the received signals is caused by the signals having traveled different propagation paths to two different points on the traveled path.

12. The method of claim 11 , wherein generating expected signal power levels of the received signals includes determining unobstructed direct electromagnetic wave propagation conditions from a transmitter to the traveled path and obstructed direct electromagnetic wave propagation conditions from a transmitter to the traveled path.

13. The method of claim 11 further comprising: determining a bias region for the first estimated track; selecting one or more LOPs, based on the bias region, to advance; and determining the track bias based on the selected one or more selected LOPs.

14. The method of claim 13 , further comprising: determining a plurality of biases; determining a final bias based on a sum of the plurality biases; and determining the second estimated track based on the sum of the plurality of biases.

15. The method of claim 14 , further comprising: weighing one or more of the plurality of biases prior to summing the plurality of biases, or weighing one or more of the plurality of biases based on an age of the one or more LOPs or on a distance of the one or more LOPs from an estimated current position.

16. The method of claim 3 , wherein receiving the signals along the traveled path includes receiving the signals at two different points along the traveled path at a same time, wherein recording signal power levels of the received signals includes recording the signal power levels of the received signals over at the two different points, and wherein the extracted feature is caused by the signals having traveled different propagation paths to the two different points on the traveled path.

17. The method of claim 16 , further comprising: identifying an expected feature based on the expected signal power levels; determining a track bias based the extracted feature and the expected feature; and generating the second estimated track based on the track bias.

18. A device comprising: a receiver to receive signals along a traveled path from a transmitter, wherein the traveled path is a path actually traveled by the receiver; a memory to record signal power levels of the received signals and a first estimated track, wherein the first estimated track includes an estimate of the traveled path; a processor to: identify an extracted feature of the signal power levels, wherein the extracted feature is caused by a propagation path between the transmitter and the receiver transitioning from a first propagation path to a second propagation path as a result of the receiver having traveled from a first point on the traveled path to a second point on the traveled path, wherein the first point is different than the second point; generate expected signal power levels of the received signals based on the first estimated track of the traveled path; and generate an updated estimated track of the traveled path based on the recorded signal power levels, a first estimated track of the traveled path, the expected signal power levels, and the extracted feature, wherein the memory is configured to store the updated estimated track, wherein the updated estimated track is more accurate than the first estimated track relative to the traveled path.

19. The device of claim 18 , wherein the receiver is configured to receive the signals over a period of time, wherein the memory records the signal power levels of the received signals over the period of time, wherein the extracted feature is caused by the signals having traveled different propagation paths to the two different points on the traveled path at two different times, and wherein the processor is configured to identify an expected feature based on the expected signal power levels, determine a track bias based the extracted feature and the expected feature, and generate the updated estimated track based on the track bias.

20. The device of claim 19 , wherein the processor is further configured to identify extracted features of the signal power levels, wherein the extracted features are caused by the signals having traveled different propagation paths to the traveled path; identify expected features based on the expected signal power levels, wherein determining the track bias includes determining the track bias based the extracted features and the expected features; and generate the updated estimated track based on the track bias, wherein each of the extracted features is caused by the signals having traveled different propagation paths from a same transmitter to the receiver.